1. Field of the Invention
The present invention relates to the manufacturing of pipes and interconnection accessories based on new thermoplastic CPVC formulations obtained through the photochlorination process of water-suspended PVC, presenting good processability and high productivity and meeting cell classification 23447-B as a compound as outlined in ASTM-D1784 standard and NMX-E-181-SCFI-2003 standard as a finished product.
2. Description of the Previous Art
Background: CPVC is a resin obtained from PVC chlorination such as described in U.S. Pat. Nos. 2,996,489, 3,100,762, 3,334,077, 3,334,078, 3,506,637, 3,534,013, 3,591,571, 4,049,517, 4,350,798, 4,377,459, 4,412,898 and 4,459,387. Its main objective is to obtain a new resin with properties that are different from PVC properties, and above all a higher thermal resistance. This means that the service condition interval widens compared to PVC and this fact has opened new fields of application for said resin.
With regard to CPVC, because it is more rigid than PVC, with higher heat distortion temperature, it is an ideal material to operate with hot or cold water in ducts and storage tanks. The high content of chlorine of the CPVC molecule compared to PVC besides conferring some favorable characteristics, also confers other characteristics that are not as desirable, i.e., the rigidity of the molecule impedes its movement and thus it is a material which is more difficult to process, and at the same time it becomes fragile and, as PVC, tends to breakdown under the high temperature conditions required for its processing. For this reason, CPVC has to be mixed with several chemical agents in order to have the desired behavior, both in the processing stage as well as during its performance as a product. Among the components added to it, thermal stabilizers are known that prevent and/or delay degradation, impact modifiers to make it less fragile and process auxiliaries as well as lubricants among other additives to obtain a good property balance.
The behavior of the product during processing and in the field depends on the concentrations of the additive types selected for a formula and, as is well known in the art, many additives have positive effects on some characteristics of the material, but at the same time show negative effects with regard to other characteristics and finally the formulator has to find the right balance to obtain a product with the desired characteristics.
Among the impact modifiers, acrylonitrile-butadiene-styrene (ABS) terpolymers and rubbers such as CPE can be used as mentioned in U.S. Pat. No. 5,591,497, but preferably their use is not recommended. The use of polyorganosiloxanes known in the art and commented in U.S. Pat. No. 5,981,663 as impact modifiers for CPVC is not recommended either. Such materials can be used from 5 to 15 parts per hundred (phr) of resin in the formula and the quantity to use depends highly on the chlorine content of the CPVC.
An important aspect to be taken into account with the polymer materials and, especially with such a rigid and viscous compound as a CPVC compound can become, is its processability. To improve said processability, several solutions are recommended in the state of the art. One of said solutions is to add materials such as plasticizers, but although they help, they have a negative effect on other properties; other mixtures of CPVC have been published, such as in U.S. Pat. No. 3,268,626, with some styrene and acrylonitrile copolymers with relatively low viscosities, together with a second butadiene and acrylonitrile polymer. In U.S. Pat. No. 3,678,132, the improvement of the CPVC processability is presented through the introduction of a Polyvinyl Chloride (PVC) mixture with an alpha methyl styrene, methyl metacrylate and acrylonitrile terpolymer and a butadiene based polymer grafted with styrene, methyl metacrylate and acrylonitrile, in proportions ensuring a better processability. Moreover, in U.S. Pat. No. 4,304,884 CPVC mixture with copolymers prepared with alpha methyl styrene, vinyl compounds selected among vinyl benzenes, acrylates and aliphatic nitriles is mentioned. All these attempts, among others, include in general the use of lower molecular weight resins, acrylic based processing aid specifically designed to improve the behavior of the material during the plastification and to improve the resin fluidity.
In order to improve the CPVC processability, a whole range of lubricants known in the art is used. However, and for the specific case of the lubricants, the general rule is to keep their concentration at the minimum level, because in high quantities problems can occur such as processing problems, thermal stability problems and the properties of the final product can deteriorate.
The whole range of possible lubricants is known in the art and although in many patents lubrication level of 5 phr are mentioned, such as in the U.S. Pat. No. 5,981,663 and in published Patent Number 2003/0157321 A1, the fact is that in none of the examples mentioned in these references, the lubrication levels are above 3 phr and this is because the general idea is to keep the lubrication level as low as possible.
It is thus an object of the present invention to supply a CPVC compound with high output capacities both for extrusion as well as for injection purposes, fulfilling classification 23447-B as a compound as outlined in ASTM-D1784 and fulfilling NMX-E-181-SCFI-2003 as a finished product.